Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$177.37	12.156%	$198.9311	$198.93	$198.95	$198.90
Purchase #2	$82.49	6.204%	$87.6077	$87.61	$87.60	$87.60
Purchase #3	$20.43	7.225%	$21.9061	$21.91	$21.90	$21.90
Purchase #4	$85.80	11.286%	$95.4834	$95.48	$95.50	$95.50
Purchase #5	$240.48	9.784%	$264.0086	$264.01	$264.00	$264.00
Purchase #6	$19.31	10.505%	$21.3385	$21.34	$21.35	$21.30
Purchase #7	$29.89	8.418%	$32.4061	$32.41	$32.40	$32.40
7 purchase totals =	$655.77		$721.6815	$721.69	$721.70	$721.60